The instant invention relates generally to pressure transducers and more particularly to a piezoresistive assembly adapted to simultaneously measure both absolute and differential pressures.
Piezoresistive sensor structures are widely used in pressure or force measuring. Generally, the prior art is replete with a number of patents which describe various configurations and methods of fabricating piezoresistive pressure sensing devices.
Generally, a piezoresistive device includes a bridge pattern of resistors which are mounted or otherwise diffused on one side of a relatively thin diaphragm member. The diaphragm which may be fabricated from silicon, and deflects upon application of a pressure thereto causes the piezoresistors to vary their magnitude according to the deflection of the diaphragm.
Differential pressure measurements can be accomplished using a differential transducer which provides an output which is the difference between two pressures. In the particular case of a gage sensor one of these pressures is atmospheric pressure and the other pressure is the pressure to be measured. In the case of the absolute pressure transducer, the output is solely indicative of a pressure applied.
Presently there are many implementations that require the measurement of both absolute and differential pressures. It is unfortunately necessary to often duplicate sensors and/or complicate associated circuitry thus resulting in elevated costs of manufacture and maintenance.
Further, the demand for pressure measuring assemblies adapted for use in hostile (high temperature and/or highly corrosive for example) environments has grown in recent years.
Commonly assigned U.S. Pat. No. 4,222,277, filed Aug. 13, 1979, entitled xe2x80x9cMedia Compatible Pressure Transducerxe2x80x9d, teaches an absolute pressure transducer which is adaptable for use in various deleterious mediums. Therein, a single wafer contains a gage sensor configuration on one portion and an absolute sensor configuration on another adjacent portion.
However, both the absolute and gage sensors of the ""277 are exposed to a single pressure. Accordingly, it is desirable, and the object of the present invention to provide a relatively inexpensive structure capable of measuring multiple absolute pressures and a differential pressure associated therewith. It is another object of the instant invention to provide a relatively inexpensive structure capable of measuring both absolute and differential pressures which is further adapted for prolonged use in a hostile environment.
A combination absolute and differential pressure sensing device including: two pressure transducers each respectively including two electrically separated half bridge piezoresistive structures; two resistors; and, a device for selectively coupling one of the half bridge piezoresistive structures of a first one of the absolute pressure transducers to two resistors to form a half-active full bridge structure adapted to measure an absolute pressure; and, one of the plurality of half bridge piezoresistive structures of the first one of the two absolute pressure transducers to one of the half bridge piezoresistive structures of a second one of the absolute pressure transducers to form a full bridge structure adapted to measure a differential pressure.